1. Technical Field
The present invention relates to wireless communications and, more particularly, to circuitry for determining received signal strength values and for controlling gain settings for amplifiers in the receive signal path.
2. Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards, including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, etc., communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of a plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via a public switched telephone network (PSTN), via the Internet, and/or via some other wide area network.
Each wireless communication device includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier stage. The data modulation stage converts raw data into baseband signals in accordance with the particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier stage amplifies the RF signals prior to transmission via an antenna.
Typically, the data modulation stage is implemented on a baseband processor chip, while the intermediate frequency (IF) stages and power amplifier stage are implemented on a separate radio processor chip. Historically, radio integrated circuits have been designed using bi-polar circuitry, allowing for large signal swings and linear transmitter component behavior. Therefore, many legacy baseband processors employ analog interfaces that communicate analog signals to and from the radio processor.
One common problem in processing a received signal in a receive signal path is that signal-to-noise ratios fluctuate according to an amount of present noise and/or according to fluctuations only in signal strength. At the same time, if an amplification level were left constant, then an amplified signal may experience clipping when noise levels exceed a certain threshold. To avoid this problem, it is possible to reduce amplification levels to avoid clipping even in situations where ambient noise levels are high. Unfortunately, however, this approach results in a received signal being amplified a lesser amount. Moreover, even without considering interference, an ingoing signal may vary in magnitude by a wide range. Accordingly, preset amplification levels would tend to under-amplify small scale signals and over-amplify large scale signals.
One design issue that is prevalent in designing a receiver relates to the effects of gain control upon signal detection. Stated differently, gain control and its detection are related in that detection will fail if a signal is clipped or not gained enough between the radio and the baseband processor. For example, if the cumulative sum of all amplification results in a signal being amplified too much, the signal will clip at an output analog-to-digital converter resulting in a loss of data. On the other hand, if a signal is not adequately amplified, then the output analog-to-digital converter will be unable to generate a digital signal that accurately reflects an in-going analog signal received at an antenna. Thus, the method and apparatus for determining an appropriate amount of gain to allow accurate signal detection is needed.
Additionally, it is a known technique to provide a training sequence in a preamble of a non-synchronous data packet. Because the training sequence includes a known pattern, a receiver may determine what types of compensation are required to accurately receive an ingoing RF signal. As data rates increase, however, the amount of time that a receiver has to properly adjust its radio front end amplification levels decreases thereby creating a need for a system and method that may respond to shorter training sequences. At the same time, there is a competing goal of designing circuits that are hardware efficient. As such, there is a need for a method and apparatus that efficiently but effectively adjust a radio front end within the required amount of time defined by a training sequence.